The Ultimate Guide to Suspension and Handling Part 1: Wheels and Tires
By Mike Kojima
Horsepower is sexy and chicks dig it, at least a lot of meatheads think that way. Making horsepower is relatively easy. A lot of competent people know how to make power, lots of it. Until drifting became the rage in this country, handling and cornering prowess was for geeks, the road racing elite and autocrossers. Handling was for dweebs that raced around cones in parking lots, or loners prowling canyon roads at night, not for cool people in the scene.
How to tune a car's suspension was an unknown art in the world of mainstream performance, simply because most people didn’t care about handling. Most people emulated the world of road racing by making their cars low. Low was cool, low was handling.
Now that drifting, Time Attack, racetrack hotlapping and autocross are becoming popular, suspension tuning and handling are becoming important items for discussion, experimentation and debate. Building handling into a car is not necessarily any more complicated than building power; it’s just that the subject is somewhat more esoteric and definitive information is not as widely available.
Finding straight-line horsepower gurus for hire to help you is relatively easy, but finding an expert to make your car corner well is a tough deal, fraught with mystery and intrigue. The solution? Make yourself the guru. If your automotive interests are greater than the one-dimensional urge to blast straight down the 1320, brag about dyno sheets on internet forums or install neon and strobe lights to your interior and undercarrage, let’s get to work. There are 4 basic steps to achieving a well handling car and in this first part of our extensive series we'll discuss the first--wheels and tires.
Get Some Sticky Tires
Tires by far are the biggest contributor to finding more cornering force. By bolting on a set of gumball tires, you can make the biggest possible single net gain in cornering power in minutes. Generally, putting the widest tires and wheels that will fit inside your wheel wells without rubbing is the way to go. Specing out an ultra-high performance tire is also important. Most of these tires can perform decently during track days and are good for autocross in SCCA's ST street classes.
If you are doing track events, autocrossing or are just plain nuts and simply have to have the most grip possible, you can try a set of DOT approved racing tires. Some of these tires are nearly useable as everyday driving tires while others grip almost like racing slicks and last about the same length of time. Below is a chart which categorizes these tires. Note that this is somewhat subjective and there is some overlap here.
Sticky Ultra High Performance Street Tire
Race Tire, Nearly Streetable, Long Wearing, Many Heat Cycles
Race Tire, Sticky Medium Wearing, Medium Heat Cycle
Race Tire, Really Sticky, Fast Wearing, Low Heat Cycles
Yokohama Advan Neova AD008 Hankook Z214 C31
Hankook Z214 C51, C71
Hankook Z214 C91
Hoosier A6, R6
Kumho Ecsta 700
Kumho Ecsta 710
Kumho XS KU36
Michelin Pilot Sport PS2
Michelin Pilot Sport Cup
BFG G-Force R1
Bridgestone Pontenza RE11
Kumho Victoracer V700
Avon Tech RA
Pirelli Pzero Corsa
Race compound DOT tires produce more road sucking grip than any suspension mod you can do but the drawbacks are many. First, these tires can be expensive; second, they wear quickly; third, the number of heat cycles that their rubber formulations can withstand before becoming oxidized and hard is limited; and fourth, many of them don’t do well in the wet and none work in the snow or ice. It is possible to end up with an expensive, fast wearing and not so grippy tire if these race tires are used on the street and subjected to many heat cycles. Most people who use these race tires have a second set of wheels and use them only for weekend warrior activities.
Within reason, put a wider wheel and tire on your car to put more rubber on the road. Generally you can stuff a tire two sizes larger than stock into most cars stock wheel wells. For instance a car that came with a 185/70-14 tire on a 5" inch wide wheel can usually easily accommodate a 205/50-15 on a 7" wide wheel with no modifications at all. On most cars you can roll the fender flange flat to get more tire clearance if needed. Do not accept any rubbing between the tire and any part of the car, be it the fender or the suspension, it can be very dangerous. When deciding which wider wheels for your car, try to stick to close to the stock proportions of offset to wheel width to maintain a reasonable scrub radius. We will explain why in later editions of our handling guide. Choose the size of your tire and wheel including the offset with this in mind for the best performance rather than going for the hella flush aesthetic unless that’s what floats your boat.
For all of our poking fun of Hella Flush, and overstreching tires on too wide wheels, stretching tires can improve response by making it harder to get sidewall flex under cornering load. Here the Cyber EVO, one of the fastest time attack cars ever built shows its stretched tires. For road racing we feel that this is not advisable due to the sensitivity to impact damage and de-beading if things are not exactly right but the Cyber EVO shows that this technique can work well. It is a trick that some autocrossers swear by as they need fast response.
Putting the tires on a wheel of the recommended width for the tire is important as well. Putting a wide tire on a narrow stock rim will cause the tread to tend to lift on the edges under side load. If you can’t get the exact wheel width recommended by the tire manufacture for your size of tire, then always err to the wider side if you have the choice. A tire that is slightly stretched on a wide wheel will be more responsive and flex less under side load than one whose sidewalls are bubbled due to too narrow of a rim. Some autocrossers looking for the maximum responsiveness out of their tires will stretch a tire on a rim as much as two inches too wide. When doing this, the rim and tire are more prone to damage and debeading under impact so this is not advisable for street use or road racing where you sometimes put wheels off the track or hit FIA curbs.
It's obvious that this isn't the greatest thing for performance.
Plus sizing, which is going to a larger diameter wheel and a low profile tire can help with faster response to steering input and less need for static negative camber for best grip due to the plus tires having a shorter and stiffer sidewall. For instance going from a 205/55-15 to a 205/40-17 on your typical FWD compact car will usually give crisper handling. Going overboard like several inches larger in your rim diameter and running ultra low profile tires generally is not always the hot tip.
Overstretched tires are prone to de-beading and damage to the tire and wheel from impact, wrong inflation pressure and side load
It is possible to over do it. Low stiff sidewalls don’t conform to bumpy surfaces easily. This makes ultra low profile tires sensitive to shock, as the super short, stiff sidewalls have very little compliance. Harsh surface inputs can make these tires skip and hop across the surface instead of digging in and finding grip making ultra low profile tires more sensitive to shock tuning. Big wheels are heavy creating a flywheel effect which is harder to accelerate and brake. Huge dubs also screw up your gear ratio contributing to sluggish acceleration.
Lastly, big heavy wheels and tires also add unsprung weight which reduces the effectiveness of the suspension. Unsprung weight is the weight of the components that are not suspended on a car. This includes the suspension arms, brakes, half of the shock absorber and the wheel and tire. Typically unsprung weight is 12-15% of the total weight of a car. For the suspension to work well, the ratio of sprung to unsprung weight must be kept as low as possible. For instance, have you ever noticed that the suspension of monster trucks hardly works? Even though they may have wheel travel measured in feet instead of inches, it’s hardly ever used and the trucks bounce and bang around like crazed Tonka toys. This is because Monster Trucks have a very high ratio of sprung to unsprung weight. Those huge earthmover tires possibly weigh more than the whole truck. When surface irregularities are hit, high unsprung weight generates significant force with an upward component which means a rough ride and difficulty keeping the rubber on the road. High unsprung weight also means that the shocks have to work much harder to damp wheel movement as well. Reducing the unsprung weight and the suspension is worked less, the ride improves and the tire can be kept in contact with the ground better.
For these reasons, putting a 215/35-18 on the same compact FWD car that worked well with a 205/50-15 will probably reduce its performance. Doing something really dumb like putting a 245/25-22 on an EVO is very detrimental to performance.
Generally for small bore naturally aspirated 4-cylinder like the older Honda Civics and Nisan Sentras, a lightweight 15x7" wheel is the best bet for performance. For larger cars about 18" is the usual practical maximum wheel diameter. Larger than this, you won’t find as many choices in sizes for true high performance tires. Wheels larger than 18" in diameter are mostly for show except in a few cases like the R35 GT-R which needs its big 20" wheels to clear its huge 15" brakes. Dub sizes don’t have ultra high performance applications either; the huge, oversized in diameter tires offered are mostly designed for the NBA player or gangsta rapper aesthetic.
Get Lightweight Wheels
The obvious way to make up for the disadvantages of increased wheel diameter and width is to use a light wheel. Light wheels are easier to accelerate and brake. They also reduce unsprung weight. Ever wonder why so many MotoIQ project cars run Volk wheels? Most Volks are forged. The forging process improves the grain structure and work hardens the metal (engineering terms for making it stronger!) It provides a superior strength-to-weight ratio. We like Enkei’s competition series wheels as well which have MAT formed rim sections. MAT helps improve the metal's mechanical properties much like forging for a fraction of the cost. Lower cost wheels are usually cast. The casting is a cheapest way to make wheels and nearly all low-priced wheels are cast aluminum.
The wheels listed below run the gamut of price point and quality but are all decent wheels with good weight.
Light wheels / low price
Enkei Racing Series wheels
5Ziggen FN01R-C, Pro Racer
Rays Gram Light C series
Team Dynamics Procomp
Team Dynamics Prorace
Work Emotion, XSA
OZ Racing Series
Very light wheels / price not considered
Volk one-piece forged
Rays Gram Light F series